In a centralized channel access system a number of users share a common channel and there is some coordination control to determine which user is going to use the system. A centralized channel access system has a central device to determine the user that has access. In wireless communications data may not be received for one or more reasons such a nearby jamming signal, noisy signal, low power transmission, etc. Hardware and software standards are provided that govern the transmission between two stations. On local area networks (LANs) data link protocols such as Token Ring, and FDDI provide the access control method (OSI layers 1 and 2) that moves packets from station to station. Some means needs to be provided to notify transmitter when data is lost. The data link protocol is a hand shaking operation with message exchanges such as “are you there?” “yes, I am”, “are you ready to receive?”, “yes, I am”, “Here it comes” plus data and “did you get it”, if the receiver did not the response “no, I didn't”, “Here it comes again” plus data and “did you get it”, if yes then “yes, I did”, “There is no more”, and then “goodbye”. Some systems may provide a negative acknowledgment that the data was lost and send that back to the transmitter. Other systems may send back a positive statement indicating what was received and nothing if it was not received.
FIG. 1 illustrates a communication system with the protocol layers. The system includes point or multipoint transceiver(s) 11 communicating with a point or multipoint transceiver(s) 13 via a wireless network including antennas 11a and 13a. Each point or multipoint 11 or 13 have at the bottom layer the physical (PHY) layer coupled to the antennas. Above the physical layer is the medium access control (MAC) sublayer. Above the MAC sublayer is a logical link control (LLC) sublayer. In the operation a series of LLC frames are passed down to a MAC sublayer as MAC service data units (MSDUs) and from the MAC sublayer to the PHY layer as MAC protocol data units (MPDUs). The MAC sublayer determines if each frame is transmitted correctly. The reception at the opposite end such as at receiver 13 the signals travel up the stack from the PHY layer to the MAC sublayer to the LLC sublayer.
The central controller may not allow the user to occupy the channel for so long as to transmit a whole MSDU so an MSDU may have to be divided into pieces of fragments, each of which is then transmitted as a separate MPDU when access is permitted. Another reason to break up into fragments is to maximize the successful transmission probability. A long packet suffers more if there are channel impairments such as noise or other interference because there is a greater chance of affecting the message. It is the responsibility of the MAC to do the fragmentation. As illustrated in FIG. 2 two numbers are needed to identify an MSDU fragment, a number for identifying the fragment out of all the fragments of the MSDU and a number for identifying the MSDU out of a series of MSDUs. An MSDU may be decomposed into a variable number of fragments. The transmitting station sends out fragments to the receiving station and fragments may be refragmented again or combined for retransmission if they were not successfully transmitted. The present invention provides a means of enabling the transmitting station to label, and the receiving station to acknowledge, the transmitted fragments, so that lost fragments can be identified and retransmitted to achieve communications reliability over an unreliable channel. Such a means is referred to as automatic repeat request. i.e., ARQ. This present application teaches an improvement for the ARQ described in IEEE 802.16ab-01/01, incorporated herein by reference.